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       dblink_get_pkey - returns the positions and field names of a relation's primary key fields


       dblink_get_pkey(text relname) returns setof dblink_pkey_results


       dblink_get_pkey provides information about the primary key of a relation in the local
       database. This is sometimes useful in generating queries to be sent to remote databases.


           Name of a local relation, for example foo or myschema.mytab. Include double quotes if
           the name is mixed-case or contains special characters, for example "FooBar"; without
           quotes, the string will be folded to lower case.


       Returns one row for each primary key field, or no rows if the relation has no primary key.
       The result row type is defined as

           CREATE TYPE dblink_pkey_results AS (position int, colname text);

       The position column simply runs from 1 to N; it is the number of the field within the
       primary key, not the number within the table's columns.


           CREATE TABLE foobar (
               f1 int,
               f2 int,
               f3 int,
               PRIMARY KEY (f1, f2, f3)
           CREATE TABLE

           SELECT * FROM dblink_get_pkey('foobar');
            position | colname
                   1 | f1
                   2 | f2
                   3 | f3
           (3 rows)